Observation of Spin-Dependent Charge Symmetry Breaking in $\hat{I}›N$ Interaction: Gamma-Ray Spectroscopy of ${}_{\hat{I}›}^4$He

Abstract

The energy spacing between the ground-state spin doublet of ${}_{\hat{I}}^4›$He(1${}^{+}$,0${}^{+}$) was determined to be $1406\pm 2\pm 2$ keV, by measuring ${\hat{I}}^3$ rays for the $1^{+}\to 0^{+}$ transition with a high efficiency germanium detector array in coincidence with the ${}^4$He$(K^{-},\ddot{I}{€}^{-})$ ${}_{\hat{I}}^4›$He reaction at J-PARC. In comparison to the corresponding energy spacing in the mirror hypernucleus ${}_{\hat{I}}^4›$H, the present result clearly indicates the existence of charge symmetry breaking (CSB) in $\hat{I}›N$ interaction. It is also found that the CSB effect is large in the $0^{+}$ ground state but is by one order of magnitude smaller in the $1^{+}$ excited state, demonstrating that the $\hat{I}›N$ CSB interaction has spin dependence.